Radio receiver



Patented Oct. 5, 1937 UNITED STATES RADIO RECEIVER Helmut Pitsch, Berlin,

Germany, assignor to Telefunken' Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application December 23, 1936, Serial No. 117,299 In Germany October 23, 1935 1 Claim.

It is known in the art that high selectance and satisfactory high-fidelity reproduction are conflicting demands seeing that, in order to obtain high selectance, the side-bands must be greatly 5 trimmed to prevent other stations from coming through, and to also prevent the production of interference notes. Where large receiver apparatus are concerned, it has, of late, become general practice to provide a band switch in order that in cases where high selectance is not such a serious desideratum, better reproduction may be obtainable by using a wider band. This is particularly useful for local reception. However, the

expenditure for switches and circuit elements rereception of local stations. However, by the ways and means known in the art such a change-over would be hard to carry into practice seeing that in case of a change to local reception the last I. F. oscillation circuit must be disconnected from the rectifier tube while in its stead a receiving oscillation circuit must be connected. On the other hand, when operating I. F. receivers there is the risk of spontaneous oscillation, in the ab-- sence of special switches, by way of the capacitance inherent in the switch contacts which, as will be remembered, are located at the grids and which thus are at an R. F. potential in reference to each other.

According to this invention, the said drawbacks are obviated. The invention consists in that in a receiver comprising a change-over switch to bridge the I. F. part, the bridging condenser (C) for the resistance (W) which is connected with the diode rectifier (G) and an I. F. oscillatory circuit (ZF) in case of I. F. reception is united by a switch S1 with the filament and therefore is connected in parallel tothe resistance (W), whereas, for local reception, the same serves as a coupling condenser in that it is connected with an oscillatory circuit (HF) of the receiver so that the diode rectification then works with a parallel arrangement of oscillatory circuit (HF), resistance (W) and diode (G).

The invention shall now be explained in more detail by reference'to the annexed drawing showing exemplified embodiments of the invention whereof Fig. 1 shows the circuit connections of a superheterodyne receiver; Fig. 2 is a modification of the circuit connections shown in Fig. 1;

receiver set would be to bridge the I. F. part for andFigs. 3 and 4 show the decoupling means for V the rectifier circuit of the receiver.

Referring to Fig. l, the mixer tube of the superheterodyne is designated by M. The incoming or signal frequency potential is fed by way of the oscillatory circuit HF and the heterodyning fre quency from osci1lator 0. The ensuing I. F. or beat frequency is then fed by way of the I. F. part Z and the oscillatory circuit ZF to the rectifier G whence the resultant A. F. is fed to the amplifier NF. The AF potential arises across the resistance W, across which is produced at the same time also a volume-control (anti-fading) potential which may be tapped at point a. The resistance W as known in the art, is shunted by a condenser C in order that the full RF voltage may be applied to the rectifier. When operated as a superheterodyne receiver, the switch S1 is therefore thrown in the lower position, while it is placed in the upper position whenever a change to local reception is to be effected. The incoming signal voltage by way of the shielded line L, without change into an intermediate frequency, is then directly fed to the rectifier, the condenser C here serving as a coupling condenser. By this change in connections, also the rectifier circuit itself is altered in that the resistance W is not connected in series with the diode D and the corresponding oscillation circuit, but rather in parallel thereto. This will be clearly seen from Fig. 2. In this drawing the I. F. part has been omitted seeing that in local reception this part is inoperative. The oscillation circuit ZF, in Fig.2, to be sure is still ahead of the diode, but this is not harmful seeing that the incoming signal frequency differs from the I. F., and since the oscillatory circuit ZF, for instance, in thep-resence of a. higher incoming frequency, acts like a capacity for RF.

Fig. 1 shows another switch S2 which is actuated simultaneously with the switch S1 and which disconnects the heating supply for the mixer tube or the whole I. F. part. Instead, the I. F. part ZF could be short circuited for local reception.

The advantages of a circuit organization as here disclosed are that the switch contact belonging to the line L, when the set is operated as a superheterodyne, is placed opposite switch contacts which are only at filament potential so that there is no risk of feedback being set up.

This circuit organization offers the further merit that when operated as a superheterodyne, that is to say, when high selectance is required, series arrangement in the rectifier circuit which is freer from damping could be resorted to.

Without the invention, in case of a change-over by switch, double-pole switching of the oscilla-' tory circuits HF and ZF would be required.

Figs. 3 and 4show that the invention will also be usable if the rectifier circuit comprises de-' coupling means of a kind known in the prior art and which in Fig. 3 consist of choke-coil Dr and the condenser C1. Fig. 4 shows the same scheme as in Fig. 3 but for local reception in order that the rectifier arrangement then obtained may be clearer. v i 7 These exemplified embodiments represent the simplest case ofa single oscillation circuit ahead of the mixer tube. Of course, even for local reception it is more advantageous to provide an 'RF stage seeing that frequently the RF voltage mixer stage could also be used for amplification in that in the plate circuit, in series with the oscillation circuit, an oscillation circuit tuned to the incoming signal frequency is included. Inasmuch as in local reception no high selectance is demanded such an oscillatory circuit may be designed in a simple and cheapimanner.

What I claim is: i

In a superheterodyne receiver 'of the type ineluding a signal input circuit, means for converting the signal energy to an intermediate frequency, an intermediate frequency transmission network, a diode detector having an input circuit tuned to said intermediate frequency and coupled to said network, and a load resistor connected in series with said detector input circuit and diode; theimprovement comprising a condenser havingone terminal thereof connected to the anode side of said diode, and switch means constructed and arranged for selectively connecting, in one position thereof, the other terminal to the diode. cathode, and in another position thereof connecting the condenser and load resistor directly across said" signal input circuitwhereby said'diode is a parallel rectification network.

HELMU'I PITSCH. 

